1. Field of the Invention
The subject invention relates to cutting heads for rotary trimmers and, more specifically, it relates to an improved cutting head for rotary trimmers using monofilament string as a means for cutting vegetation. The subject invention represents an improvement over presently existing cutter head designs and allows for a smoother, more efficient feedout of the monofilament string during operation of the cutter head.
2. Description of the Related Art
Flail feedout means for mowing and trimming devices used to trim grass, weeds, and other vegetation, of the rotary type equipped with flexible cord-like flails formed of generally cylindrical fibers, are well known in the art. Grass and weed cutters of this general type are widely known and the subject of various patented devices including those described in Ballas et al., U.S. Pat. No. 3,826,068; Mizuno et al., U.S. Pat. No. 4,020,552; Prouix, U.S. Pat. No. 4,097,991; Perdue, U.S. Pat. No. 4,134,204; Toro, Belgium Patent No. 852,150; and Prouix, U.S. Pat. No. 4,259,782. Such devices are available on the market having automatic flail feedout mechanisms which respond to a bump on the ground intentionally applied by the operator or by the application of force applied thereto by some mechanical arrangement. Such mechanisms usually consist of a dog or friction clutch located between a spool of flail and the case thereabout through which the flail is fed. By bumping an extension of the spool on the ground, the friction clutch is disengaged for a length of time dependent on the duration of the bump. The dog clutch released by the bump then abruptly engages at the next opportunity to feed out flail in segment lengths which are related to the engagement points of the dog clutch. Such dog clutches have outwardly extending ribs which engage inwardly extending abutment tangs and therefore depend upon a skillful bump when it is desired that they move only one segment. However, friction within the device and overzealous bumping can result in two or more line segments being fed out, especially when the device has been in use and the corners on the ribs and tangs have worn so that positive engagement is no longer assured.
An improved flail feedout mechanism for a rotary mower is disclosed in the above-mentioned U.S. Pat. No. 4,259,782, the disclosure of which is incorporated herein by reference. This prior art mower includes a handle with drive means which are connected to a spinning housing which contains a spool of one or more coils of filaments used as flails, an orifice through the housing for each coil for extending the flail outwardly into cutting position, and means which normally restrict movement between the spool and the housing but can be released a predetermined rotational distance so that additional flail can be fed out of the orifice. These last-mentioned means include, as part of the spool, a downwardly projecting bumper which is normally used to space the flail above the surface on which vegetation is being cut. The spool, bumper and the intermediate member, as an assembly, are spring loaded downwardly with respect to the spinning housing. Extending inwardly from the intermediate cylinder are tangs which ride in a serpentinous cam slot in a cam member fixed to the housing. When the bumper is bumped on the ground, the intermediate cylinder is moved upwardly so that its tangs ride up relatively vertical cam surfaces until they reach spiral surfaces which extend downwardly to the next vertical cam surfaces. The net effect is that the spool, connected to the intermediate members, and the housing, connected to the cam member, rotate relative to each other to allow a predetermined length of flail to feed out as a result of centrifugal force acting on the flail. Since a serpentinous cam is used, a single bump can produce only one segment of flail feedout, and does so without the crunching engagement of the prior art dog clutches.
Despite the improvement in the rotary mowing and trimming device of U.S. Pat. No. 4,259,782, the specific construction of the tangs and the serpentinous cam slot in that device is designed to result in stress concentrations in the engaging members and, as a result, an abrupt and discontinuous operation of the feedout assembly which results in potential wear of the assembly parts, as well as non-smooth operation of the mowing device.
Accordingly, it is an object of the subject invention to provide an improved automatic flail feedout device which is reliable, easy and economical to manufacture, and which operates smoothly so that its performance does not degrade with use.
It is a further object of the subject invention to provide a mower which feeds out a predetermined amount of flail when desired in a smooth and consistent manner, without resulting in stress concentrations on the individual parts forming the feedout assembly.
The cutting head for a rotary trimmer of the subject invention is an improvement of the feedout mechansim of U.S. Pat. No. 4,259,782 and employs the same basic structural architecture. Briefly, the subject trimmer includes a hollow handle with an attached drive means that is connected to a spinning housing. The housing has a spool containing one or more coils of string used as filaments for cutting vegetation. A pair of orifices is oppositely positioned on the spool for guiding the exposed filament to the proper cutting position.
The feedout assembly includes a follower member having a number of tangs that have a base that is wider than the rounded end to form a taper from the base to the tip thereof. The follower member is coupled to a cam having offset tangs for controlling the amount of filament fed out of the cutting head to a predetermined length. The offset prongs are also configured to have a base that is wider than the rounded tip thereof to form a taper from the base to the tip. Furthermore, the taper of each offset prong is complimentary to the taper of each tang. The configuration of the subject invention results in better force distribution and the reduction of stress concentrations when the tangs and prongs engage each other, thereby resulting in a smoother feedout of the filament and a structurally enhanced feedout assembly. A biasing spring maintains the follower member and the cam properly positioned within the feedout assembly so that the filaments are fed out upon tapping of the subject cutting head against the ground.